AD8318_15 Datasheet, PDF (1/24 Pages) Analog Devices – 1 MHz to 8 GHz, 70 dB Logarithmic Detector/Controller

1 MHz to 8 GHz, 70 dB
Logarithmic Detector/Controller
AD8318
FEATURES
Wide bandwidth: 1 MHz to 8 GHz
High accuracy: ±1.0 dB over 55 dB range (f < 5.8 GHz)
Stability over temperature: ±0.5 dB
Low noise measurement/controller output (VOUT)
Pulse response time: 10 ns/12 ns (fall/rise)
Integrated temperature sensor
Small footprint LFCSP
Power-down feature: <1.5 mW at 5 V
Single-supply operation: 5 V @ 68 mA
Fabricated using high speed SiGe process
APPLICATIONS
RF transmitter PA setpoint control and level monitoring
RSSI measurement in base stations, WLAN, WiMAX, and
radars
GENERAL DESCRIPTION
The AD8318 is a demodulating logarithmic amplifier, capable
of accurately converting an RF input signal to a corresponding
decibel-scaled output voltage. It employs the progressive
compression technique over a cascaded amplifier chain, each
stage of which is equipped with a detector cell. The device is
used in measurement or controller mode. The AD8318
maintains accurate log conformance for signals of 1 MHz to
6 GHz and provides useful operation to 8 GHz. The input range
is typically 60 dB (re: 50 Ω) with error less than ±1 dB. The
AD8318 has a 10 ns response time that enables RF burst
detection to beyond 45 MHz. The device provides unprece-
dented logarithmic intercept stability vs. ambient temperature
conditions. A 2 mV/°C slope temperature sensor output is also
provided for additional system monitoring. A single supply of
5 V is required. Current consumption is typically 68 mA. Power
consumption decreases to <1.5 mW when the device is disabled.
The AD8318 can be configured to provide a control voltage
to a VGA, such as a power amplifier or a measurement output,
from Pin VOUT. Because the output can be used for controller
applications, wideband noise is minimal.
Rev. B
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TEMP
FUNCTIONAL BLOCK DIAGRAM
VPSI
ENBL
TADJ
VPSO
TEMP
SENSOR
GAIN
BIAS
SLOPE
IV
VSET
INHI
INLO
DET
DET
DET DET
IV
VOUT
CLPF
CMIP
Figure 1.
CMOP
2.4
6
2.2
5
2.0
4
1.8
3
1.6
2
1.4
1
1.2
0
1.0
–1
0.8
–2
0.6
–3
0.4
–4
0.2
–5
0
–6
–65 –60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –5 0 5 10
P_IN (dBm)
Figure 2. Typical Logarithmic Response and Error vs. Input Amplitude at 5.8 GHz
In this mode, the setpoint control voltage is applied to VSET.
The feedback loop through an RF amplifier is closed via VOUT,
the output of which regulates the amplifier output to a magnitude
corresponding to VSET. The AD8318 provides 0 V to 4.9 V
output capability at the VOUT pin, suitable for controller
applications. As a measurement device, Pin VOUT is externally
connected to VSET to produce an output voltage, VOUT, which
is a decreasing linear-in-dB function of the RF input signal
amplitude.
The logarithmic slope is nominally −25 mV/dB but can be
adjusted by scaling the feedback voltage from VOUT to the
VSET interface. The intercept is 20 dBm (re: 50 Ω, CW input)
using the INHI input. These parameters are very stable against
supply and temperature variations.
The AD8318 is fabricated on a SiGe bipolar IC process and is
available in a 4 mm × 4 mm, 16-lead LFCSP for the operating
temperature range of –40^oC to +85^oC.
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